Surface treatment agent and surface treatment method

Abstract

A surface treatment agent and a surface treatment method capable of imparting excellent corrosion resistance while enhancing adhesion between a surface of a metal substrate and a resin-containing layer. The surface treatment agent for treating a surface of a metal substrate includes an acrylic resin having a carboxyl group and a hydroxyl group, an oxazoline group-containing compound and metal particles containing at least one of Nb, Ca and Nd. The metal may be in the form of a niobium oxide sol.

The invention claimed is: 
     
       1. A surface treatment agent for treating a surface of a metal substrate to form a surface-treated film, the surface treatment agent comprising:
 an acrylic resin having a carboxyl group and a hydroxyl group, an oxazoline group-containing compound and metal particles, 
 wherein the metal particles are particles containing at least one metal selected from the group consisting of Nb, Ca and Nd, 
 wherein an amount of the metal particles is from 0.05 to 2.5% by mass in terms of metal oxide relative to total amount of the surface treatment agent, 
 wherein a mass ratio of the total amount of the content of the acrylic resin having a carboxyl group and a hydroxyl group and the content of the oxazoline group-containing compound to the content of the metal particles in terms of metal oxide [(the total amount of the content of the acrylic resin having a carboxyl group and a hydroxyl group and the content of the oxazoline group-containing compound)/(the content of the metal particles in terms of metal oxide)] is from 0.4 to 7.5, and 
 wherein the surface-treated film contains metal derived from the metal particles in the amount of 20 to 600 mg/m 2  in terms of metal oxide. 
 
     
     
       2. The surface treatment agent according to  claim 1 , wherein the metal particles are in the form of a niobium oxide sol. 
     
     
       3. A surface treatment method, which comprises applying the surface treatment agent according to  claim 1  onto a surface of a metal substrate to form the surface-treated film.